Many techniques are known and used for manufacture of coils for mechanical, electrical, and electromagnetic applications. For example, an elongated flexible structure such as a thread or wire may be helically wrapped around a cylindrical surface to define the coil. Alternatively, an electrical conductor may be deposited in a helical path around a surface. However, when the desired coil is is for a microsystem and has many turns having a diameter on the order of a few millimeters, and a conductor diameter on the order of tens of micrometers, conventional fabrication techniques are not sufficient.
Alternative techniques are therefore being explored to meet the manufacturing requirements of microsystems. While a large variety of microcomponents and microelectromechanical devices have been demonstrated in recent years, most fabrication has involved inherently planar techniques, such as x-ray or optical lithography. Features are defined in polished substrates or thin film layers by exposure of a resist (using a mask) and etching. However, there is a desire to fabricate more complex shaped features in a variety of ceramics, metals and polymers. For example, nonprismatic features and nonplanar workpieces are needed for a variety of devices such as micro-fluidic sensors, microinductors, and microactuators.
Recently, several groups have demonstrated techniques that fabricate curvilinear features. This includes micro-contact printing which applies a xe2x80x98two dimensionalxe2x80x99 lithographic master to a substrate such as a cylinder (see R. J. Jackman et al, xe2x80x9cDesign and Fabrication of Topologically Complex, Three-dimensional Microstructures,xe2x80x9d Science, 1998, 280, 2089-2091), and laser chemical vapor deposition which involves direct writing of materials via pyrolysis or photodecomposition of precursor gases. (See J. Maxwell et al., xe2x80x9cRapid Prototyping of Functional Three-Dimensional Microsolenoids and Electromagnets by High-Pressure Laser Chemical Vapor Deposition,xe2x80x9d Proc. Solid Freeform Fabrication Symposium, 1998; 529-536.) Other inherently planar techniques such as LIGA are also being adapted to produce overhangs and curved features, as reported by T. R. Christenson, xe2x80x9cAdvances in LIGA-based post-mold fabrication,xe2x80x9d Proc. of SPIE Micromachining and Microfabrication Process Technology IV, 1998; 3511, 192-203 and others. Nevertheless, additional capabilities are required, since many of the aforementioned techniques are limited in dimensionality, material complexity or microstructure control.
Focused ion beam (FIB) sputtering is attractive for fabricating micron-size tools or instruments that can precisely define curved features (See M. Vasile et al., xe2x80x9cMicrofabrication techniques using focused ion beams and emergent applicationsxe2x80x9d, Micron 30 (June 1999) 235-244). Commercial focused ion beam systems are quite powerful, providing 10 nA currents, 10 nm spot sizes, and 10 nm pixel spacings. Most importantly, focused ion beam sputtering can be used to create and align a number of nonplanar features, such as facets required on micro-shaping tools. Several studies demonstrate FIB-sputtered microgears, microwrenches, microscalpels, and nanoindenters. The intent of current work is to fabricate micron size features over centimeter length scales in reasonable time. Further, it is expected that tools having xcx9c25 xcexcm diameters are mechanically robust and reproducibly define microscopic features. Recent work shows that ground metal micro-end mill tools having cutting diameters of xcx9c50-100 xcexcm successfully machine small grooves in stainless steel workpieces, as reported by T. Schaller et al., xe2x80x9cMicrostructure grooves with a width of less that 50 xcexcm cut with ground hard metal micro end millsxe2x80x9d, J. Prec. Eng. 1999; 23, 229-235.
Additional studies demonstrate that xcx9c25 xcexcm diameter, FIB-fabricated micro-end mills machine trenches in polymethyl methacrylate (PMMA) and metal workpieces. Material has been mechanically removed from metal alloy workpieces at a rate of 2xc3x97104 xcexcm3/sec for over an hour. In comparison, typical ion beam sputter removal rates are xcx9c0.1-20 xcexcm3/sec using commercial FIB systems. In the present work, focused ion beam sputtering is combined with ultra-precision machining in order to create complex features in a variety of materials. This includes micromachining approximately 15-100 xcexcm wide, curvilinear features in planar and cylindrical workpieces.
A method for filling small grooves is the Damascene process, where a groove is made in a substrate, the substrate and groove are coated with a material, and the material is removed from the substrate but remains in the groove. See P. Andricacos et al., xe2x80x9cDamascene copper electroplating for chip interconnectionsxe2x80x9d, IBM Journal of Research and Development, Vol. 42, No. 5, 1998. While the Damascene process has been utilized for industrial purposes on planar substrates by the semiconductor industry, it has not been employed on curved surfaces other than to provide artistic decoration to objects.
It is an object of this invention to create very small patterns in non-planar surfaces by machining the features in the surface, filling the machined features with a second material, and treating the surface to remove any excess second material.
It is a further object of this invention to create very small coils on round substrates by machining a helical groove in the substrate, filling the groove with a conductive material, and removing any conductive material that overflows the groove.
To achieve the foregoing and other objects, and in accordance with the purpose of the present invention, as embodied and broadly described herein, the present invention may comprise a process for fabricating coils including providing a curved substrate made of a first material and having a surface extending along and about an axis; forming a helical groove in the curved surface along and around the axis, said groove extending at least one turn around the axis; and filling the groove with a second material different from the first material to form a coil of second material in said first material.
Additional objects, advantages, and novel features of the invention will become apparent to those skilled in the art upon examination of the following description or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.